Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $239.85   6.456%   $255.3347   $255.33   $255.35   $255.30  
  Purchase #2 $119.83   12.117%   $134.3498   $134.35   $134.35   $134.30  
  Purchase #3 $55.86   13.353%   $63.319   $63.32   $63.30   $63.30  
  Purchase #4 $223.53   13.664%   $254.0731   $254.07   $254.05   $254.10  
  Purchase #5 $177.47   12.462%   $199.5863   $199.59   $199.60   $199.60  
  Purchase #6 $204.96   13.641%   $232.9186   $232.92   $232.90   $232.90  
  Purchase #7 $232.26   6.225%   $246.7182   $246.72   $246.70   $246.70  
  7 purchase totals = $1,253.76       $1,386.2997   $1,386.30   $1,386.25   $1,386.20